GB2095279A - Process for refining coal-based heavy oils - Google Patents

Abstract

A coal-based heavy oil is refined so as to remove quinoline insolubles and provide a product hydrocarbon mixture suitable for making carbon stocks, by (a) providing a residual coal-based heavy oil 1 which has been freed of volatile components which have boiling points of up to a temperature of from 200 DEG C to 270 DEG C, (b) mixing the said residual coal- based heavy oil with a ketone-type solvent 2 having a boiling point of less than 200 DEG C to form an insoluble precipitate and a supernatent liquid, (c) separating the said insoluble precipitate from the supernatent liquid, (d) treating the said supernatent liquid to recover the said solvent therefrom thereby leaving a hydrocarbon mixture. The removal of the particular range of volatile compounds provides for the formation of a precipitate which is readily separable. The product hydrocarbon mixture is easily processed by distillation under reduced pressure to produce a hydrocarbon product suitable for making high-grade carbon stocks. <IMAGE>

Description

SPECIFICATION Process for refining coal-based heavy oils The present invention relates to a process for refining coal-based heavy oils, and particularly relates to such a process to produce hydrocarbon products which are suitable for the production of high-grade carbon stocks.

Carbon stocks such as readily graphitizable acicular coke, isotropic carbon and high-grade activated carbon are very useful for example in making ultra high power graphitic electrodes. Hitherto carbon stocks have been produced from a variety of raw materials e.g. from petroleum-based and coalbased heavy oils, and synthetic polymers. Petroleum-based heavy oils and coal-based heavy oils have been the most popular raw materials because of their low cost and high carbonization yields, the coal-based heavy oils in particular resulting in high carbonization yields.

However the use of both petroleum-based heavy oils and coal-based heavy oils have disadvantages. For example petroleum-based heavy oils from most sources contain sulphur which is a very undesirable component, and the number of sources capable of producing low suiphur-containing petroleum-based heavy oils are limited. Although coal-based heavy oils have very low sulphur contents and provide very high carbonization yields, they contain minute amounts of fine, inactive carbonaceous substances, especially insoluble quinolines which if not removed, detrimentally affect the graphitizing properties of the coal-based heavy oils. This is particularly undesirable when attempting to produce therefrom high-grade carbon stocks (e.g. containing acicular coke and isotropic carbon).

Methods have been devised for removing insoluble quinolines from conventional coal-based heavy oils so as to enable such oils to produce high-grade carbon stocks. Such methods may be classified into four categories: (1) Methods which involve subjecting the coal-based heavy oils to a thermal treatment, thereby enlarging the insoluble quinoline particles and facilitating separation thereof (for example as disclosed in Japanese Patent specifications Nos. 32722/1972 and 4334/1958); (2) Methods which involve mixing the coal-based heavy oils with an organic solvent, thereby inducing precipitation of insoluble compounds (including quinolines) and permitting separation thereof (for example as disclosed in Japanese Patent specifications JA-OS 102303/1977):: (3) Methods which involve mixing the coal-based heavy oils with an aliphatic solvent, stirring the mixture at an elevated temperature and allowing the stirred mixture to stand and cool, thereby inducing precipitation of the insoluble compounds (including quinolines) and permitting separation thereof (for example as disclosed in Japanese Patent specifications No. 26481/1974 and JA-OS 98720/1976, and (4) Methods which involve mixing the coal-based heavy oils with an aliphatic solvent and an aromatic solvent, thereby inducing precipitation of the contained insoluble compounds (including quinolines) and permitting separation thereof (for example as disclosed in Japanese Patent specification JA-OS 78201/1977).

Such methods have however not been acceptable in practice. In Type (1) methods, since the insoluble particles precipitated therein have extremely small diameters, their separation proceeds at a low speed and with poor efficiency, and during separation the filter used becomes clogged. Further since the coal-based heavy oil must be centrifuged or filtered at an elevated temperature to provide it with a lowered viscosity, the operation entails expensive equipment and high costs of maintenance. In Type (2) methods, since the amount of organic solvent used therein generally is from 10 to 100 times that of the coal-based heavy oils, these methods are very costly. Moreover since the precipitated insoluble particles produced by these methods have extremely small particle diameters, their separation is achieved with a very low efficiency.In Type (3) methods, since the precipitation of insoluble particles therein generally occurs slowly at normal room temperature, it is necessary that the mixture of coal based heavy oil and solvent is stirred for several hours at a temperature of not less than 2000C and left to stand and cool until precipitation of the insoluble particles occurs, followed by the separation of the precipitated insolubles. Finally in Type (4) methods, although the precipitated insolubles have relatively large particle diameters and efficient separation is achieved, the amounts of aromatic solvent and aliphatic solvent generally added in amounts is several times that needed to treat petroleum-based heavy oils.Since these added solvents are expensive, the treatment is not economical because of the cost of the devices needed to recycle the solvents, and even if the solvents are not recycled, the operation still proves uneconomical because the yields of carbonization are inevitably lowered.

Moreover, since the heavy oil is mixed with two types of solvents, the equipment used must have a proportionately larger size for handling a fixed volume of heavy oil, and therefore these methods prove less advantageous for commercialization. In addition, the quality control of the solvents, which is necessitated when the solvents are cyclically used, becomes difficult.

Thus in general, none of the methods so far proposed have proved commercially feasible for the removal insoluble quinolines from conventional coal-based heavy oils.

It is an object of the present invention to provide a commercially acceptable method for refining coal-based heavy oils so as to easily remove insoluble quinolines therefrom, and to provide a commercially acceptable method for treating coal-based heavy oils so as to produce hydrocarbon products suitable for the production of high quality carbon stocks.

According to the present invention the insoluble quinolines in coal-based heavy oils can be effectively removed therefrom by first providing a coal-based heavy oil from which the volatile components therein having a boiling point from 2000C to 2700C have been removed (such treated coal-based heavy oils being hereinafter referred to as "residual coal-based heavy oils"), then mixing the residual coal-based heavy oils with ketone-type solvents to form an insoluble precipitate (insoluble quinolines and gummy, tacky substances) in a supernatent liquid, separating the precipitate from the supernatent liquid and then recovering from the supernatent liquid the ketone-type solvent to provide a hydrocarbon solution which is suitable for further procesing into high quality carbon stocks.The insoluble quinolines are esily removed from the supernatent liquid because they adhere to the said gummy, tacky substances which thereby develop into a stable precipitate of coarser grains due to the adhesion of the non-viscous insoluble quinolines thereto.

The residual coal-based heavy oil used in the process is the heavy oil fraction which remains after an initial coal-based heavy oil raw material, e.g. a coal tar such as a high-temperature tar or a lowtemperature tar produced as a byproduct during the carbonization of coal, or a coal liquefaction product, has been treated to remove therefrom the volatile fraction composed of components which have boiling points of up to at least 2000C and at most 2700 C. In a preferred embodiment of the invention, the initial raw material is heated up from its initial boiling point up to a temperature of at least 2000C and at most 2700C, preferably between 2000C and 2300C, and the associated volatile components allowed to escape, thereby leaving a residual coal-based heavy oil for use according to the invention.

If the initial raw material is heated to less than 2000C and only the volatile components therein removed which have boiling points between the initial boiling point of the initial raw material and such a reduced temperature, the remaining fraction, if used in the remaining steps of the invention will require the use of greatly increased amounts of ketone-type solvent, the formed precipitate particles will have such small diameters (measured in tens of microns) that separation thereof from the supernatent liquid will be difficult, and recovery of the ketqne-type solvent hampered.However if the initial raw material is heated to temperatures in excess of 2700C so that the volatile components therein which have boiling points between the initial boiling point of the initial raw material and the achieved temperature of greater than 2700C are removed, the remaining fraction will produce large insoluble precipitates in the form of black, gummy, viscous materials which will clog the pipes and pumps of the equipment used. In addition some of the components intended to remain in the filtrate (pitch components) will precipitate out thus reducing the yield of the final product.

Examples of ketone-type solvents which are used in the invention are methyl ethyl ketone, isopropyl methyl ketone, methylpropyl ketone, diethyl ketone, pinavolone, isobutyl methyl ketone, diisopropyl ketone, methyl butyi ketone and butyrone; methyl vinyl ketone, mesityl oxide and methyl heptanone; cyclopentanone and cyclohexanone; and ethyl amyl ketone and hexyl methyl ketone; and various combinations of two or more thereof. In order to be readily separated from the residual coalbase heavy oils by distillation once the insoluble quinolines hve been removed therefrom, the ketonetype solvent used will desirably have a boiling point of less than 2000C, preferably below 1000C.When the ketone-type solvent has a boiling point of not less than 2000C, the separation of this solvent from the residual coal-based heavy oil (from which the insoluble quinolines have been removed) is difficult.

Consequently it is undesirable to utilize such solvents in a cyclic process.

The mixing together of the residual coal-based heavy oil of the invention and the ketone-type solvent may be effected at room temperature and at atmospheric pressure. Stirring of the mixture is continued until the insoluble precipitate which will include insoluble quinolines, is separated out in the form of a stable granular solid. Usually the insoluble precipitate is converted into readily separable coarse solid particles in a few minutes.

The amount of the ketone-type solvent added to the residual coal-based heavy oil of the invention is preferably from 10% to 60%, particularly from 30% to 50% by weight based on the weight of the total resultant mixture. When this amount exceeds 60% the insoluble precipitate tends to be converted into a gummy viscid susbtance which lacks fluidity, which susbtance will adhere to the equipment and clog the piping, and will generally obstruct the smooth operation of the equipment. Further because the precipitate occurs in an excess amount relative to that of the initial residual coal-based heavy oil, even the components expected to remain in the filtrate will be removed as extraneous matter in conjunction with the precipitate, with the result that the yield of the process will be lowered.If the amount is less than 10%, the resultant insoluble precipitate in the form of finely divided particles tends to occur in a very small amount, making its separation from the supernatant liquid difficult. The fact that the removal of the insoluble quinolines is advantageously accomplished by use of a very small amount of the ketonetype solvent constitutes one of the preferred features of the process of the invention.

Since the granular solid formed in accordance with the process of this invention possesses a large particle diameter and therefore permits the precipitation to proceed at a high speed, the separation of the solid precipitate is readily accomplished by standing or by centrifuging. When the separation is effected by filtration, since the solid particles have large diameters, the passage of the filtrate through the filter may proceed smoothly and thus the solid particles can be separated quickly. Methods of separation may be adopted in various suitable combinations. With conventional processes, the mixture which is subjected to separation must be treated at an elevated temperature or under increased pressure to lower the viscosity of the raw material and facilitate the separation.The process of the present invention has an advantage that the residual coal-based heavy oil of the invention has its viscosity lowered by the addition of the low-boiling ketone-type solvent, thus the separation of the insoluble precipitate is thoroughly carried out without requirig the application of heat to the mxiture which is to be separated.

After the insoluble precipitate which includes finely divided insoluble quinolines originally contained in a very low concentration in the residual coal-based heavy oil of the invention, has been separated out, the solvent remaining in the resultant mixed solution filtrate can easily be separated by distillation because the solvent component itself has a low boiling point and the heavy oil component does not contain any volatile components of the boiling points indicated. Thus the solvent can easily be recovered and returned to a storage tank for re-use. The remaining hydrocarbon product is suitable for further treatments so as to manufacture high-grade carbon stocks.

The process of this inventionwill now be further illustrated by reference to the accompanying drawing and the following working examples and comparative experiments.

The drawing is a flow diagram for treating a residual coal-based heavy oil according to the invention wherein a storage tank 1 is shown which contains the residual coal-based heavy oil and a storage tank 2 containing the ketone-type solvent. The residual coal-based heavy oil and the ketone type solvent are conveyed to a stirring tank 3 where they are combined and mixed, and the resultant mixture then conveyed to a separator 4 where the insoluble precipitates (including insoluble quinolines) are separated from the supernatent liquid or filtrate (the precipitates being removed from the bottom of the separator). The filtrate is then conveyed to a recovery tower 5 where it is treated so as to recover the desired hydrocarbon product (refined tar) and solvent, the solvent being returned to tank 2.

The following Examples of the invention and Comparative Experiments are provided.

EXAMPLE 1 A coal-based heavy oil in the form of coal tar containing 3.6% of insoluble quinolines and possessing the properties shown in Table 1 , was heated to 2700 so as to remove the volatile components having boiling points of up to 2700C. A residual coal-based heavy oil was left. The residual coal-based heavy oil was then mixed at room temperature and atmospheric pressure with an equal amount by weight of methyl ethyl ketone having a boiling point of about 800 C. A dark brown granular solid of about 1.0 mm diameter was formed. When the mixed solution was passed through a filter of 0.25 mm mesh at room temperature to separate out the granular solid, the granular solid could be separated in an amount of 5.6% based on the initial weight of the residual coal-based heavy oil.

The filtrate remaining after the separation of the granular solid was distilled under atmospheric pressure to recover the methyl ethyl ketone. The remaining solution was then distilled under reduced pressure to expel the oil fraction boiling at temperatures within the range 2700C to 3500C (calculated for atmospheric pressure) and a black pitch remained. As is shown in Table 1, the pitch had excellent qualities and was free of insoluble quinolines.

COMPARATIVE EXPERIMENT 1 When 10% by weight of the residual coal-based heavy oil used in Example 1, was mixed and stirred at room temperature and at atmospheric pressure with 90% by weight of pyridine having a boiling point of about 11 60C, no significant insoluble precipitates were formed, and when the resultant mixed solution was filtered as in Example 1, no separation of soild occurred. Thus it was difficult to separate the insoluble quinolines by filtration. The pitch which was obtained by concentrating the filtrate in the same manner as in Example 1 possessed properties as shown in Table 1, from which it is seen that quinoline solubles were contained therein.

TABLE 1

Raw Example Comparative Material 1 Experiment 1 I Residual coal-based heavy oil 100 50 10 Mixing ratio Methyl ethyl ketone - 50 (S/o) Pyridine - - 90 Yield of granular solid recovered (O/o) 5.6 0 n+ieptane insolubles 32.4 68.5 70.0 Properties Insolubles Benzene of raw content in insolubles 9.1 21.9 22.7 material solvent ( /O) and pitch Quinoline insolubles 3.6 0 4.8 Softening point (OC) 22 72 76 Yield of Pitch ( /O) 60 66 EXAMPLE 2 A coal-based heavy oil in the form of coal tar containing 3.2% of insoluble quinoline and possessing the properties shown in Table 2, was heated to a temperature of 2300C so as to remove the volatile components having boiling points of up to 2300C. A residual coal-based heavy oil was left. 60% by weight of the residual coal-based heavy oil and 40% by weight of acetone having a boiling point of 56 OC were combined and stirred at room temperature and atmospheric pressure.A dark brown granular solid similar to the granular solid of Example 1 , was formed. When the resultant mixed solution was treated in a centrifuge rotating to produce 2000 G for one minute to separate the granular solid, there was obtained a granular precipitate in a yield of 4.7% based on the residual coal-based heavy oil used as the raw material.

The supernatant liquid was distilled under atmospheric pressure to recover acetone. The remaining solution was then distilled under a reduced pressure to separate a fraction boiling at temperatures within the range of from 2300C to 3500C, and a black pitch was obtained. This pitch had properties as shown in Table 2, from which it is seen that this pitch contained no insoluble quinoline whatever.

COMPARATIVE EXPERIMENT 2 At normal room temperature and at atmospheric pressure, 30% by weight of the residual coalbased heavy oil used in Example 2 and 70% by weight of benzene having a boiling point of 800 C, were mixed and stirred. When the resultant solution was centrifuged under the same conditions as in Example 2, there was obtained an insoluble precipitate in a yield of 0.3% based on the residual coal based heavy oil raw material. The supernatent liquid obtained was distilled under atmospheric pressure to recover the benzene. When the remaining solution was concentrated in the same manner as in Examples 1 and 2, there was obtained a black pitch. This pitch exhibited properties shown in Table 2, from which it is seen that the pitch contained insoluble quinoline.

TABLE 2

-------- -------- Raw Example Comparative Material 2 Experiment 2 Residual coal"based heavy oil 100 60 30 Mixing ratio Acetone - 40 (%) Benzene 70 Yield of precipitate (O/o) 1 4.7 08 n3-leptane insoiubles 29,8 69.7 70.3 Properties Insolubles Benzene of raw content in insolubles 4.5 22.3 23.1 material solvent (%) and pitch Quinoline insolubles 3.2 0 3.5 Softening point (OC) 6 73 75 Yield of pitch (%) - 53 58 As is evident from the Examples of the invention, the separation of quinoline insolubles by filtration which has been heretofore found difficult to achieve can be effectively carried out by the process of the invention with a filter of about 0.25 mm mesh without causing clogging. Thus the removal of quinoline insolubles can be accomplished very easily. Also by means of a centrifuge the removal of insoluble quinolines can be obtained quickly with a low centrifugal force. The process of this invention is highly advantageous for the purpose of commercial refinement of coal-based heavy oil.

EXAMPLE 3 A liquefaction product boiling at temperatures of not less than 2300C was obtained by extraction of coal with a solvent contained 12% of insoluble quinoline such as undissolved coal and ashes as shovvn in Table 3.

When 65% by weight of this liquefaction product and 35% by weight of isopropyl methyl ketone having a boiling point of 950C were mixed and stirred at 600C for 30 minutes, there was formed a dark brown granular solid, which settled to the bottom when the solution was allowed to stand and cool.

When the supernatent liquid was separated by decantation, the sediment was obtained in a yield of 18% by weight based on the liquefaction product. The liquefaction product remaining after the removal of the sediment was distilled to recover the isopropyl methyl ketone, and was further distilled under reduced pressure to recover fractions boiling up to 4500C (as computed for atmospheric pressure).

There was thereby obtained a black pitch in a yield of 32% by weight based on the liquefaction product as the raw material. This black pitch exhibited properties shown in Table 3, from which it is seen that it was completely free of insoluble quinolines.

COMPARATIVE EXPERIMENT 3 Under the same conditions as in Example 3, the liquefaction product of coal used therein and about twice as much isopropyl methyl ketone were mixed, stirred, allowed to stand and cool. A black gummy viscous matter became firmly attached to the agitation blades and within the stirrer. After the supernatent liquid was separated by decantation, the viscous matter was obtained in a yield of 32% by weight based on the liquefaction product as the raw material.

When the supernatent liquid was distilled in the same manner as in Example 3, a black pitch was obtained in a yield of 14% by weight based on the raw material, having properties as shown in Table 3.

TABLE 3

Raw Example Comparative Material 3 Experiment 3 Residual coal-based heavy oil 100 65 30 Mixing ratio ( /O) Isopropyl methyl ketone - 35 70 Yield of precipitate (%) ~ 18 32 nÇeptane insolubles 41 76 71 Properties Insolubles Benzene of raw content in insolubles 22 32 21 material solvent ( /O) and pitch Quinoline insolubles 12 0 0 Softening point (OC) 45 105 70 Yield of Pitch (%) - 32 14 From the working Examples of the invention, it is found that the insoluble precipitates separated by the process of the present invention were in the form of coarse, non-viscous grains that were easily settled. Since the components of the coal-based heavy oil to be desirably retained in the filtrate were not precipitated, the yield was increased over the yields obtained in the Comparative Experiments involving the removal of gummy, viscid matter. Moreover the insoluble quinolines were removed in the form of precipitates. All these results indicate that the process of this invention suits commercial applications.

Claims (11)

1. A process for refining coal-based heavy oils which comprises (a) provided a residual coal-based heavy oil which has been freed of volatile components which have boiling points of from 2000C to 2700 C, (b) mixing the said residual coal-based heavy oil with a ketone-type solvent having a boiling point of less than 2000C to form an insoluble precipitate and a supernatent liquid, (c) separating the said insoluble precipitate from the supernatent liquid, (d) treating the said supernatent liquid to recover the said solvent therefrom thereby leaving a hydrocarbon mixture.

2. A process according to Claim 1, wherein the said residual coal-based heavy oil starting material is provided by heating a coal-based heavy oil to a temperature of between 2000C and 2700C and allowing the volatile components to escape therefrom.

3. A process according to Claim 2, wherein the said coal-based heavy oil is heated to a temperature of between 2000C and 2300C such that residual coal-based heavy oil has been freed of volatile components having boiling points between the boiling point of the heavy oil and up to not less than 2000C and not more than 2300 C.

4. A process according to any of Claims 1 to 3, wherein the said coal-based heavy oil is a coal tar.

5. A process according to any of Claims 1 to 3, wherein the said coai-based heavy oil is a coal liquefaction product.

6. A process according to any of Claims 1 to 5, wherein the said ketone-type solvent has a boiling point of not more than 1000C.

7. A process according to any of Claims 1 to 6, wherein said ketone-type solvent is acetone, methyl ethyl ketone, isopropyl methyl ketone, methyl propyl ketone, diethyl ketone, pinacolone, isobutyl methyl ketone, diisopropyl ketone, methyl butyl ketone, butyrone, methyl vinyl ketone, mesityl oxide, methyl heptanone, cyclopentanone, cyclohexanone, ethyl amyl ketone or hexyl methyl ketone, or a mxiture of two or more thereof.

8. A process according to any of Claims 1 to 7, wherein the proportion of the ketone-type solvent to be added to said residual coal-based heavy oil is within the range 10% to 60% by weight based on the total weight of the resultant mixture.

9. A process according to Claim 8, wherein said proportion is within the range of from 30% to 50% by weight, based on the total weight of the resultant mixture.

10. A process according to any of Claims 1 to 9, substantially as hereinbefore described with particular reference to the Examples.

11. A process according to any of Claims 1 to 10, wherein the product hydrocarbon mxiture is distilled under reduced pressure to provide a hydrocarbon product suitable for making high quality carbon stocks.